2.2.1 Context Format

The context output format shows several lines of context around the
lines that differ. It is the standard format for distributing updates
to source code.

To select this output format, use the
--context[=lines] (-C lines)
or -c option. The
argument lines that some of these options take is the number of
lines of context to show. If you do not specify lines, it
defaults to three. For proper operation, patch typically needs
at least two lines of context.